Hi, may I know car seat is to be used from newborn to when? And booster seat from how old to how old?

I would say check the manual for the car seat or the manufacturer's website. Usually they would state the weight of the kid coz age is not really a good gauge. Kids come in different sizes. My girl is coming to 15 months but she's about 10 months old size and weighs 7kg.

Car seat from newborn to 6. We used infant booster till baby was 7 months